1. Field of Invention
The invention relates to an ink droplet ejecting method and apparatus of an ink jet type.
2. Description of Related Art
According to a known ink jet printer, the volume of an ink flow path is changed by deformation of a piezoelectric ceramic material, and when the flow path volume decreases, the ink present in the ink flow path is ejected as a droplet from a nozzle, while when the flow path volume increases, the ink is introduced into the ink flow path from an ink inlet. In this type of a printing head, a plurality of ink chambers are formed by partition walls of a piezoelectric ceramic material, and an ink supply device, such as ink cartridges are connected to one end of each of the multiple ink chambers, while at the opposite end of each of the ink chambers are provided ink ejecting nozzles (hereinafter referred to simply as xe2x80x9cnozzlesxe2x80x9d). The partition walls are deformed in accordance with printing data to make the ink chambers smaller in volume, whereby ink droplets are ejected onto a printing medium from the nozzles to print, for example, a character or a figure.
As this type of an ink jet printer, a drop-on-demand type ink jet printer which ejects ink droplets is popular because of a high ejection efficiency and a low running cost. As an example of the drop-on-demand type there is known a shear mode type using a piezoelectric material, as is disclosed in Japanese Published Unexamined Patent Application No. Sho 63-247051.
As shown in FIGS. 7A-8, this type of an ink droplet ejecting apparatus 600 comprises a bottom wall 601, a top wall 602 and shear mode actuator walls 603 located therebetween. The actuator walls 603 each comprise a lower wall 607 bonded to the bottom wall 601 and polarized in the direction of arrow 611 and an upper wall 605 formed of a piezoelectric material, the upper wall 605 being bonded to the top wall 602 and polarized in the direction of arrow 609. Adjacent actuator walls 603, in a pair, define an ink chamber 613 therebetween, and next adjacent actuator walls 603, in a pair, define a space 615 which is narrower than the ink chamber 613.
A nozzle plate 617 having nozzles 618 is fixed to one end of each of the ink chambers 613, while to the opposite end of each of the ink chambers is connected an ink supply source (not shown). On both side faces of each actuator wall 603 are formed electrodes 619 and 621, respectively, as metallized layers. More specifically, the electrode 619 is formed on the actuator wall 603 on the side of the ink chamber 613, while the electrode 621 is formed on the actuator wall 603 on the side of the space 615. The surface of the electrode 619 is covered with an insulating layer 630 for insulation from ink. The electrode 621 which faces the space 615 is connected to a ground 623, and the electrode 619 provided in each ink chamber 613 is connected to a controller 625 which provides an actuator drive signal to the electrode.
The controller 625 applies a voltage to the electrode 619 in each ink chamber, whereby the associated actuator walls 603 undergo a piezoelectric thickness slip deformation in directions to increase the volume of the ink chamber 613. For example, as shown in FIG. 8, when voltage E(V) is applied to an electrode 619c in an ink chamber 613c, electric fields are generated in directions of arrows 631 and 632 respectively in actuator walls 603e and 603f, so that the actuator walls 603e and 603f undergo a piezoelectric thickness slip deformation in directions to increase the volume of the ink chamber 613c. At this time, the internal pressure of the ink chamber 613c, including a nozzle 618c and the vicinity thereof, decreases. The applied state of the voltage E(V) is maintained for only a one-way propagation time T of a pressure wave in the ink chamber 613. During this period, ink is supplied from the ink supply source.
The one-way propagation time T is a time required for the pressure wave in the ink chamber 613 to propagate longitudinally through the same chamber. Given that the length of the ink chamber 613 is L and the velocity of sound in the ink present in the ink chamber 613 is a, the time T is determined to be T=L/a.
According to the theory of pressure wave propagation, upon the lapse of time T or an odd-multiple time thereof after the above application of voltage, the internal pressure of the ink chamber 613 reverses into a positive pressure. In conformity with this timing, the voltage being applied to the electrode 621c in the ink chamber 613c is returned to 0(V). As a result, the actuator walls 603e and 603f revert to their original state (FIG. 7A) before the deformation, whereby a pressure is applied to the ink. At this time, the above positive pressure and the pressure developed by reverting of the actuator walls 603e and 603f to their original state before the deformation, are added together to afford a relatively high pressure in the vicinity of the nozzle 618c in the ink chamber 613c, whereby an ink droplet is ejected from the nozzle 618c. An ink supply passage 626 communicating with the ink chamber 613 is formed by members 627 and 628.
Heretofore, when this kind of ink droplet jet apparatus 600 prints while the resolution varies, it is necessary to obtain dot diameters matched with respective resolutions by changing the volume of each droplet of ink. As a method of changing the volume of a droplet of ink, there is a known method of changing the volume of droplet of ink by changing the voltage value of a jet pulse. In that case, a plurality of voltage sources are required which makes the ink droplet jet apparatus unavoidably expensive.
Also, as shown in Japanese Published Unexamined Application No. Hei 6-84073, there is a known method in which a time period ranging from the trailing edge of a pulse voltage to the leading edge of the next pulse voltage is set to xc2xd of the natural vibration period of a nozzle portion, considering an influence of meniscus vibration resulting from ink-jetting. However, according to this method, for the purpose of effectively utilizing the energy required when the pulse voltage rises, the vibration of the next ink-jetting period is overlapped on the vibration generated when a piezoelectric element returns after the ink-jetting vibration was stopped. Thus, this method does not provide a countermeasure executed in the continuous vibration periods at a high printing frequency.
Moreover, as shown in Japanese Published Unexamined Patent Application No. Sho 61-120764, there is a known method in which a drive signal for a piezoelectric element is controlled with reference to a dot interval in such a manner that the volume of droplets of ink becomes constant regardless of the dot interval. However, this known method is also not able to change resolutions of continuous dots.
The invention provides an ink droplet ejecting method and apparatus in which volumes of droplets of ink may be controlled arbitrarily with ease without changing the voltage value of a jet pulse and allowing a desired resolution to be printed.
According to an aspect of the invention, there is provided an ink droplet ejecting method in which a pressure wave is generated within an ink chamber by applying a jet pulse signal to an actuator which changes the capacity of the ink chamber by applying pressure to the ink thereby jetting droplets of ink from a nozzle. The ink droplet ejecting method includes jetting droplets of ink by applying a single jet pulse or a plurality of jet pulses to the actuator at a predetermined timing period in accordance with a printing command for a single dot or a plurality of continuous dots, and changing the predetermined timing period in response to a desired volume of ink droplets. In this method, by setting a timing period of a jet pulse signal, that is, setting the printing frequency to a predetermined value corresponding to a multiple of a time T in which a pressure wave within the ink chamber propagates one-way, a volume of droplet of ink per dot to be jetted may be controlled, and it becomes possible to execute printing with a dot diameter corresponding to a particular resolution.
Also, according to another aspect of the invention in the ink droplet ejecting method, the printing frequency of the predetermined timing period is set to be a reciprocal of an even-number multiple of the time T in which a pressure wave propagates within the ink chamber one-way when the ink droplet volume of each dot is increased. In this method, by setting the printing frequency to a predetermined value, it is possible to increase the speed of droplets of ink per dot to be jetted and to also increase a volume of each droplet.
Also, according to another aspect of the invention in the ink droplet ejecting method, a printing frequency of the predetermined timing period is set to be a reciprocal of an odd-number multiple of the time T in which a pressure wave propagates within the ink chamber one-way when the ink droplet volume of each dot is decreased. In this method, by setting the printing frequency to a predetermined value, it is possible to lower the speed of droplets of ink per dot to be jetted and to decrease the volume of each droplet.
According to another aspect of the invention, the ink droplet ejecting method includes jetting droplets of ink by applying a single jet pulse or a plurality of jet pulses to the actuator at a predetermined timing period in accordance with a printing command for a single dot or a plurality of continuous dots and changing the timing corresponding to a multiple of a time T in which a pressure wave within the ink chamber propagates one-way in response to a printing density. In this method, the timing period (i.e., printing frequency) is set to a predetermined value relative to a multiple of the time T, whereby a droplet volume suitable for printing at a desired printing density may be obtained.
According to another aspect of the invention, in the ink droplet ejecting method, a printing frequency of the predetermined timing period is set to be a reciprocal of an even-number multiple of the time T in which a pressure wave propagates within the ink chamber one-way when the printing density is high. Alternatively, the printing frequency of the predetermined timing period is set to be a reciprocal of an odd-number multiple of the time T in which a pressure wave propagates within the ink chamber one-way when a printing density is low. In this method, by setting a printing frequency to a predetermined value in response to a high or low printing density, it is possible to increase or decrease the speed and volume of droplets of ink per dot to be jetted.
According to another aspect of the invention, an ink droplet ejecting apparatus is provided which includes an ink chamber containing a quantity of ink, an actuator for changing the capacity of the ink chamber, a driving power source for applying an electrical signal to the actuator, and a controller that increases the capacity of the ink chamber by applying a jet pulse signal to the actuator from the driving power source to generate a pressure wave within the ink chamber. The pressure wave creates pressure to the quantity of ink contained in the ink chamber and decreases the capacity from an increased state to a natural state after an odd-number multiple of T has elapsed (where T represents a time in which the pressure wave propagates within the ink chamber one-way), thereby jetting droplets of ink. The controller jets droplets of ink by applying a single jet pulse signal or a plurality of jet pulse signals to the actuator from the driving power source at a predetermined timing period in accordance with a printing command for a single dot or a plurality of continuous dots and changes the timing corresponding to a multiple of a time T in which a pressure wave within the ink chamber propagates one-way in response to a desired ink droplet volume for each dot.
Also, according to another aspect of the invention in the ink droplet ejecting apparatus, a printing frequency of the predetermined timing period is set to be a reciprocal of an even-number multiple of the time T in which a pressure wave propagates within the ink chamber one-way when the ink droplet volume of each dot is increased.
Also, according to an aspect of the ink droplet ejecting apparatus of the invention, the printing frequency of the predetermined timing period is set to be a reciprocal of an odd-number multiple of the time T in which a pressure wave propagates within the ink chamber one-way when the ink droplet volume of each dot is decreased.
Also, according to another aspect of the invention, the controller jets droplets of ink by applying a single jet pulse signal or a plurality of jet pulse signals to the actuator from the driving power source at a predetermined timing period in accordance with a printing command for a single dot or a plurality of continuous dots and changes the timing corresponding to a multiple of a time T in which a pressure wave within the ink chamber propagates one-way in response to a printing density.
According to another aspect of the invention, the printing frequency of the predetermined timing period may be set to a range centered around a reciprocal of an even-numbered multiple of the time T in which a pressure wave propagates within the ink chamber one-way when the printing density is increased. The range may be defined as (2Nxe2x88x920.4)xc3x97T to (2N+0.4)xc3x97T, wherein N is an integer.
In addition, the printing frequency of the predetermined timing period may be set to be a range centered around a reciprocal of an odd-numbered multiple of the time T in which a pressure wave propagates within the ink chamber one-way when the printing density is decreased. The range may be defined as (2Nxe2x88x921.4)xc3x97T to (2Nxe2x88x920.6)xc3x97T, wherein N is an integer.
Also, according to another aspect of the ink droplet ejecting apparatus of the invention, the printing frequency of the predetermined period timing is set to be a reciprocal of an even-number multiple of the time T in which a pressure wave propagates within the ink chamber one-way when the printing density is high, and the printing frequency of the predetermined timing period is set to be a reciprocal of an odd-number multiple of the time T in which a pressure wave propagates within the ink chamber one-way when the printing density is low.
As described above, according to the ink droplet ejecting method and apparatus of the invention, if the timing period of the jet pulse signal (i.e., the printing frequency) is set to a predetermined value, then without changing the voltage value of the jet pulse, the volume of droplet of ink per dot to be jetted may be controlled easily and arbitrarily, thereby making it possible to print dots with a desired resolution. Then, when the volume of the droplets of ink of each dot increases, the printing frequency of the timing period is set to the reciprocal of an even-numbered multiple of the time T in which the pressure wave propagates within the ink chamber. When the volume of droplet of ink of each dot is decreased, the printing frequency of the timing period is set to the reciprocal of the an odd-numbered multiple of the time T in which the pressure wave propagates within the ink chamber. In this manner, printing according to a desired printing density or desired printing resolution, is possible.